基于微面元理论的分层材质建模与绘制技术研究

Predicting reflectance from layered materials is one of the hotspots and difficulties of computer graphics research. Since layered materials are omnipresent in our everyday life, the usage of such type of materials in CG applications can significantly improve the photorealism of the final rendering results. In this project, we will study the modeling and rendering techniques of layered materials based on microfacet theory. Specifically, we would like to investigate how to obtain the normal distribution function, the Fresnel reflection term, and the shadowing-masking term for layered materials with multiple rough surface boundaries, and analyze the influence of multiple internal reflections, light scattering and absorption of participating medium on the determination of these terms. In addition, our reflectance model based on microfacet theory will be extended to handling multiple layers with the help of the adding-doubling method. Finally, we would like to explain the effectiveness and efficiency of our reflectance model via applying it in both offline renderers and real-time rendering applications. Compared with conventional layered reflectance models, our model based on microfacet theory has the advantages of efficiency, uniformity, lightweight, and scalability. To summarize, our research of layered materials based on microfacet theory is of important theoretical significance and practical value.

分层材质建模与绘制是目前计算机图形领域研究的热点和难点。由于分层材质能够更精确地描述现实世界中的材质，其在图形绘制中的应用可以显著提高绘制结果的物理真实感。本项目将从微面元理论的角度研究分层材质的建模与绘制技术，详细探讨基于微面元理论的材质模型中法向分布、Fresnel反射和微面元间阴影遮挡等在扩展到处理分层材质时的计算方式，着重讨论多次内反射、层内介质散射和吸收对次表面反射效果的影响，并基于adding-doubling方法推广到处理多层分层材质。最后，通过在离线绘制引擎和实时绘制场景中的应用来验证本项目提出的分层材质模型的有效性和高效性。相比于传统的分层材质模型，基于微面元理论的分层材质模型具有高效性、统一性、轻量级以及可扩展性等优势。本项目是材质建模与绘制方面的基础性研究工作，具有重要的学术意义和应用价值。

分层材质建模与绘制是目前计算机图形领域研究的热点和难点。由于分层材质能够更精确地描述现实世界中的材质，其在图形绘制中的应用可以显著提高绘制结果的物理真实感。本项目从微面元理论的角度研究分层材质的建模与绘制技术，详细探讨了基于微面元理论的材质模型中法向分布、Fresnel反射和微面元间阴影遮挡等在扩展到处理分层材质时的计算方式，着重讨论多次内反射、层内介质散射和吸收对次表面反射效果的影响。在此基础上，我们提出了扩展法向分布函数（ENDF）的概念，并采用扩展法向分布函数高效处理次表面反射。针对逆反射材质和特效涂料材质，我们基于扩展微面元理论提出了相应的高真实感绘制算法。最后，通过在离线绘制引擎和实时绘制场景中的应用验证了本项目提出的复杂材质建模与绘制方法的有效性和高效性。相比于传统的模型，基于微面元理论的材质模型具有高效性、统一性、轻量级以及可扩展性等优势。本项目是材质建模与绘制方面的基础性研究工作，具有重要的学术意义和应用价值。